1. Field of the Invention
The present invention relates generally to methods, apparatus and systems for measuring at least one characteristic of a subsurface barrier. Particularly, the methods, apparatus, and systems of the present invention relate to measuring at least one characteristic of an interlocking structure formed between adjacent adjoined casing sections that form, at least partially, a barrier for waste containment.
2. State of the Art
Containment, management, and disposal of various types of waste, such as chemical, nuclear, and other potentially harmful types of waste are recognized, longstanding problems. It is also well recognized that buried waste may often include heavy metals such as mercury or cadmium, carcinogenic materials such as trichloroethylene, radioactive materials, or other hazardous substances. Further, hazardous materials within buried waste may be leached (i.e., carried from within a liquid) therefrom, into surrounding soil and into the groundwater. Because water is used for human consumption and for agriculture, contamination of groundwater by leaching is a major concern.
However, the contamination caused by buried waste may not be limited solely to groundwater. For instance, contaminated groundwater may be carried into other waterways such as streams, rivers, and lakes, thus polluting those waterways and leading to poisoning of plant and animal life. In addition, polluted waterways pose a threat to humans as well, particularly in the case of waterways and bodies of water used for recreational purposes or as sources of drinking or irrigation water.
Also, while many of the problems associated with buried waste concern the effect of leachate on water systems, buried waste may also emit gas phase contaminants that may cause deleterious effects if not contained and managed. For instance, such gas phase contaminants may pollute the soil and the groundwater, and may build up to unsafe pressures which could ultimately result in explosion or pollution of the atmosphere by venting of the gas.
Accordingly, a variety of methods and devices have been devised to attempt to resolve the problems related to buried waste. These remedies may be broadly grouped into the categories of remediation and containment. Generally, remediation focuses on processes designed to change the chemical composition of a contaminated material or contaminant to a more benign chemical composition, while containment remedies seek to isolate contaminants and contaminated material within an area or remove them from an area.
Remediation approaches such as biological treatments, thermal processes, and chemical processes may be problematic for a variety of reasons. In particular, many remediation techniques may be expensive and potentially hazardous. Further, it may be difficult to verify the effectiveness of many remediation treatments. Also, determining the proper or optimum remediation technique for a given contamination scenario may be, in itself, a complex and time-consuming process.
Containment, barrier, or in situ approaches are problematic as well. One known containment approach is simply to dig up and remove the contaminated soil for treatment or disposal. This approach is expensive and time-consuming and often accomplishes little more than moving the problem to another location. Of course, finding an acceptable ultimate disposal location is another significant impediment to movement of a contaminated region. Other containment approaches may involve installing vertical barriers, horizontal barriers, or both types of barriers around the buried waste. In theory, this approach is attractive because it does not require digging up or otherwise disturbing the buried waste.
However, conventional containment or barrier systems suffer from a variety of inadequacies including a lack of durability, corrosion resistance, and structural integrity. These inadequacies are a function of numerous factors associated with the environment in which the containment or barrier systems are located including, but not limited to: exposure to harsh chemicals such as concentrated saline solutions, saturated calcite and gypsum solutions; exposure to extreme thermal gradients; and exposure to stresses induced by shifting in the earth. In addition, conventional barrier systems may suffer from inadequate ability to monitor or verify the integrity thereof as well as inadequate reparability thereof if a failure should occur.
Accordingly, recently, containment systems that are designed to contain, collect, or process effluent which would otherwise escape from a zone containing waste materials, have been developed. One such containment system is disclosed in U.S. Pat. No. 6,575,663 to Kostelnik, et al., assigned to the assignee of the present invention, the disclosure of which is incorporated in its entirety by reference herein. More particularly, U.S. Pat. No. 6,575,663 discloses a barrier comprising a series of adjacent casing strings that are interlocked with one another and may be filled with a barrier filling material to form a substantially continuous wall.
Also, U.S. Pat. No. 5,800,096 to Barrow discloses a subsurface barrier having a number of interconnected columns. In addition, U.S. Pat. No. 5,800,096 to Barrow discloses that the interconnected region between two interconnected columns may be filled with wax, grout, polymer, or other viscous sealer via pipes disposed proximate to the interconnected region and having outlets directed toward the interconnected region.
While the above-mentioned exemplary containment systems may form a relatively stable and corrosion resistant containment system, it may be desirable to monitor the effectiveness or integrity of the containment system after formation or during formation thereof. For instance, it may be desirable to determine the presence of deficiencies in the materials used to form a barrier. Similarly, it may be desirable to detect leaks through the barrier which may carry contaminated materials thereacross.
For instance, U.S. Pat. No. 6,575,663 also discloses a “smart casing” that may include joint integrity sensors comprising acoustic/ultrasonic time domain reflectometry sensors that detect cracks and large voids in structures such as smart casing sections or optical fiber sensors which may indicate strain measurements in smart casing sections and may indicate the presence of voids and cracks therein.
U.S. Pat. Nos. 6,016,714 and 6,648,552 to Smith, each of which are assigned to the assignee of the present invention and each of the disclosures of which is incorporated in its entirety by reference herein, each discloses placement of conductors for detecting any strain, i.e., a change in dimension, which takes place in the material of a barrier. Specifically, strain will generally elongate the conductors where the strain occurs and this will result in a change in the characteristic impedance of the affected conductors. U.S. Pat. Nos. 6,016,714 and 6,648,552 to Smith disclose that such a change in characteristic impedance can be measured with electrical time domain reflectometry; thus, indication of strain and the location of such strain may be identified and data might advantageously be collected via a computer-based data acquisition system.
In view of the conventional apparatus, methods, and systems for monitoring or verifying the integrity of waste containment structures, it may be desirable to provide improved methods, apparatus, and systems for monitoring the integrity of a waste containment structure, particularly a substantially continuous barrier formed of adjacent casing strings.